US20240255270A1 - Reducing stray magnetic field effect on an angle sensor - Google Patents
Reducing stray magnetic field effect on an angle sensor Download PDFInfo
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- US20240255270A1 US20240255270A1 US18/162,780 US202318162780A US2024255270A1 US 20240255270 A1 US20240255270 A1 US 20240255270A1 US 202318162780 A US202318162780 A US 202318162780A US 2024255270 A1 US2024255270 A1 US 2024255270A1
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
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- G01D5/142—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices
- G01D5/145—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable using electric or magnetic means influencing the magnitude of a current or voltage using Hall-effect devices influenced by the relative movement between the Hall device and magnetic fields
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
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- G01D5/00—Mechanical means for transferring the output of a sensing member; Means for converting the output of a sensing member to another variable where the form or nature of the sensing member does not constrain the means for converting; Transducers not specially adapted for a specific variable
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Definitions
- a magnetic-field angle sensor measures a direction of a magnetic-field vector through 360° in an x-y plane.
- a magnetic-field angle sensor may be used to detect an angular position of a rotating magnet.
- the presence of stray magnetic fields i.e., magnetic fields coming from other sources than a desired target) can increase an angle error of the angle sensor.
- the angle error is defined to be the difference between an actual position of a magnet and a position of the magnet as measured by the angle sensor.
- an angle sensor includes a first linear sensor and a second linear sensor.
- a first magnetic-field direction of a target magnet measured by the first linear sensor is substantially equal to a second magnetic-field direction of the target magnet measured by the second linear sensor.
- the first linear sensor, the second linear sensor and the target magnet are on an axis.
- the angle sensor determines an angle of a magnetic field.
- an angle sensor configuration in another aspect, includes a first coil, a second coil parallel to the first coil and an angle sensor disposed between the first coil and the second coil.
- the angle sensor configured to determine an angle of a magnetic field.
- an angle sensor configuration includes an angle sensor, a first magnet having a first outward magnetized pole along a first axis away from the angle sensor and a second magnet opposite the first magnetic.
- the second magnet has a second outward magnetized pole along the first axis away from the angle sensor.
- the angle sensor configuration further includes a third magnet having a first inward magnetized pole along a second axis toward the angle sensor and a fourth magnet opposite the third magnetic.
- the third magnet has a second inward magnetized pole along the second axis toward the angle sensor.
- the angle sensor is disposed between the first, second, third and fourth magnets. The angle sensor configured to determine an angle of a magnetic field.
- FIG. 1 is a diagram of an example of stacked two-dimensional (2D) linear sensors forming an angle sensor to reduce a stray magnetic field effect;
- FIG. 2 is a diagram of example of stacked 2D linear sensor package configuration
- FIG. 3 is a diagram of an example of magnetic field directions for one of the stacked 2D linear sensors closer to the magnet target;
- FIG. 4 is a diagram of an example of magnetic field directions for one of the stacked 2D linear sensors further to the magnet target;
- FIG. 5 is a diagram of an example of magnetic field directions for the 2D stacked linear sensors
- FIG. 6 is a diagram of an example of an angle sensor configuration with two cosine coils to reduce a stray magnetic field effect
- FIG. 7 is a diagram of an example of a circuit representation of FIG. 6 having two bridges
- FIG. 8 A is a graph of an example of outputs of the two bridges in FIG. 7 ;
- FIG. 8 B is a graph of an example of the angle error for the angle sensor configuration of FIG. 6 ;
- FIG. 9 is a diagram of another example of an angle sensor configuration with two cosine and two sine coils to reduce a stray magnetic field effect
- FIG. 10 is a circuit representation of FIG. 9 having one bridge
- FIG. 11 is a diagram of an example of an angle sensor configuration with inward and outward magnetized pole magnets to reduce a stray magnetic field effect
- FIG. 12 is a diagram of the inward and outward magnetized pole magnets of FIG. 11 overlaid with an example of a level plot of magnetic field amplitudes;
- FIG. 13 is a diagram of FIG. 12 with example locations for magnetoresistance elements
- FIG. 14 A is a diagram of an example of a cosine bridge at locations in FIG. 13 ;
- FIG. 14 B is a diagram of an example of a sine bridge at locations in FIG. 13 ;
- FIG. 15 A is a graph of example of outputs for the sine and cosine bridges of FIGS. 14 A and 14 B ;
- FIG. 15 B is a graph of example of Hall signals
- FIG. 15 C is a graph of an example of an output signal of an angle sensor
- FIG. 15 D is a graph of an example of an angle error for the angle sensor configuration of FIG. 11 ;
- FIG. 16 is a graph of an example of stray magnetic field induced angle error for the configuration in FIG. 11 ;
- FIG. 17 is a diagram of FIG. 13 with additional examples locations for magnetoresistance elements
- FIG. 18 A is a diagram of an example of a cosine bridge at locations in FIG. 17 ;
- FIG. 18 B is a diagram of an example of a sine bridge at locations in FIG. 17 ;
- FIG. 19 is a graph of an example of maximum error over a composite angle
- FIG. 20 is a graph of an example of misplacement induced angle error
- FIG. 21 is a graph of an example of stray magnetic field induced angle error for the configuration in FIG. 17 ;
- FIG. 22 is a diagram of FIG. 17 with additional examples locations for magnetoresistance elements arranged in a circle;
- FIG. 23 is a graph of an example of angle error versus target phase for different number of magnetoresistance elements used.
- FIG. 24 is a graph of an example of misplacement induced angle error.
- FIG. 25 is a graph of an example of stray magnetic field induced angle error for the configuration in FIG. 22 .
- stray magnetic field sometimes referred to as a “stray field”
- a reduced stray magnetic field effect contributes to reducing angle errors in the angle sensor.
- magnetic-field sensing element is used to describe a variety of electronic elements that can sense a magnetic field.
- the magnetic-field sensing element can be, but is not limited to, a Hall Effect element, a magnetoresistance element, or a magnetotransistor.
- Hall Effect elements for example, a planar Hall element, a vertical Hall element, and a Circular Vertical Hall (CVH) element.
- magnetoresistance elements for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ).
- the magnetic field sensing element may be a single element or, alternatively, may include two or more magnetic field sensing elements arranged in various configurations, e.g., a half bridge or full (Wheatstone) bridge.
- the magnetic field sensing element may be a device made of a type IV semiconductor material such as Silicon (Si) or Germanium (Ge), or a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb).
- a type IV semiconductor material such as Silicon (Si) or Germanium (Ge)
- a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb).
- some of the above-described magnetic-field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic-field sensing element, and others of the above-described magnetic-field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic-field sensing element.
- planar Hall elements tend to have axes of sensitivity perpendicular to a substrate
- metal based or metallic magnetoresistance elements e.g., GMR, TMR, AMR
- vertical Hall elements tend to have axes of sensitivity parallel to a substrate.
- two-dimensional (2D) linear sensors may be used together to function like an angle sensor.
- a first two-dimensional (2D) linear sensor 14 and a second 2D linear sensor 18 are vertically aligned on an axis 20 with a magnet target 10 .
- An arrow 12 indicates an in-plane magnetization of the magnet target 10 .
- the first 2D linear sensor 14 is disposed along a first plane (not shown) and the second linear sensor is disposed along a second plane (not shown) and the first plane and the second plane are each perpendicular to the axis 20 .
- An ellipse 22 represents a high-field magnetic flux line and an ellipse 24 represents a low-field magnetic flux line.
- the first 2D linear sensor 14 experiences a higher magnetic field amplitude than the second 2D linear sensor 18 .
- the magnetic field amplitude decreases when distance increases.
- the 2D linear sensors 14 , 18 have a linear range equal to the maximum field range from the target plus twice a maximum amplitude of a stray magnetic field, which allows the 2D linear sensors 14 , 18 avoid saturation.
- the stacked 2D linear sensors 14 , 18 allow for the detection of the amplitude and direction of the magnetic field generated by magnetic target 10 at two locations where the magnetic field direction is identical at both locations, but the magnetic field amplitude varies.
- the useful signal is the amplitude difference of the detected magnetic fields from these two locations.
- an example of a configuration to package the first and second 2D linear sensors 14 , 18 is a package 200 .
- the package 200 includes a first die 32 having the first 2D linear sensor 14 on a top surface, a second die 36 having the second 2D linear sensor on a bottom surface and a printed circuit board (PCB) 42 .
- PCB printed circuit board
- a spacer 28 separates (e.g., by about 25 microns) the first die 32 from the second die 36 .
- the second die 36 may be a flip-chip structure that is connected to the PCB 42 using solder balls 34 .
- a bonding wire 44 connects the PCB 42 to the first 2D linear sensor 14 .
- the first linear sensor 14 and the second linear sensor 18 are spaced apart by about 1 millimeter. In other embodiments, multiple bonding wires (not shown) connect the PCB 42 to the first 2D linear sensor 14 .
- the package 200 is an example of placing the 2D linear sensors 14 , 18 as far apart from each other as possible in the same package.
- System optimization may include optimizing the signal assuming the air gap constraints, the sensor linear range, and the maximum distance between the two sensors imposed by the packaging constraints.
- each of the 2D linear sensors 14 , 18 includes a magnetic-field sensing element.
- the magnetic-field sensing element is a magnetoresistance element (e.g., TMR or GMR).
- FIG. 3 depicts fields sensed by the first 2D linear sensor 14 .
- An arrow 302 indicates a target magnetic field from the magnetic target 10 and an arrow 306 represents a stray magnetic field.
- An arrow 304 represents the total field (i.e., the target magnetic field arrow 302 plus the stray field arrow 306 ).
- FIG. 4 depicts fields sensed by the second 2D linear sensor 18 .
- An arrow 402 indicates a target magnetic field from the magnetic target 10 and an arrow 406 represents the stray magnetic field.
- An arrow 404 represents the total field (i.e., the target magnetic field arrow 402 plus the stray magnetic field arrow 406 ).
- FIGS. 3 and 4 are not drawn to the same scale. That is, arrow 306 and arrow 406 should be the same size since the magnetic stray field is in a common mode (i.e., the same in all space of the application).
- FIG. 5 depicts magnetic fields experienced by the first 2D linear sensor 14 and the second 2D linear sensor 18 .
- the arrows 302 , 402 are parallel to each other and the difference of the target magnetic fields (i.e., difference of the arrows 302 , 402 ) is depicted by an arrow 500 parallel to the arrows 302 , 402 .
- the total magnetic field arrows 304 , 404 at the first 2D linear sensor 14 and the second 2D linear sensor 18 respectively are not parallel to the target magnetic fields 302 , 402 because of the stray magnetic field.
- FIG. 6 another example of a configuration to reduce stray magnetic field effects is a configuration 600 .
- the configuration 600 includes an angle sensor 604 between a cosine coil 602 a and a cosine coil 602 b .
- detection of a magnetic field occurs at higher frequencies where there are no stray magnetic fields.
- the magnetic field is modulated using the cosine coils 600 a , 600 b as an emitter and the angle of the magnetic field is detected.
- the coils 602 a , 602 b are attached to a rotating device (not shown) that rotates about the axis 610 . In one embodiment, the coils 602 a , 602 b rotate about the axis at a frequency below 100 KHz.
- a circuit representation of the configuration 600 is a circuit 700 .
- the circuit includes the coils 602 a , 602 b and an angle sensor 604 ′, which is an example of the angle sensor 604 ( FIG. 6 ).
- the angle sensor 604 ′ includes a modulator 702 that modulates the coils 602 a , 602 b at a modulation frequency.
- the angle sensor 604 ′ also includes a cosine bridge 706 and a sine bridge 708 that are modulated by the modulator 702 by the modulation frequency.
- the cosine bridge 706 and the sine bridge 708 are perpendicular to one another and have a reference (sensitive) axis perpendicular to one another. That is, the cosine bridge 706 is most sensitive along an x-axis and the sine bridge 708 is most sensitive along the y-axis.
- the cosine bridge 706 and the sine bridge 708 demodulate the magnetic field signal generated by the cosine coils 602 a , 602 b .
- the x-axis and y-axis projections of the detected magnetic field are obtained, i.e. the cosine and the sine of the measured magnetic field angle (multiplied by the field amplitude).
- FIG. 8 A an example of an output of the cosine bridge 706 is depicted by the curve 802 and an example of an output of the sine bridge 708 is depicted by the curve 804 .
- the cosine bridge 706 and the cosine bridge 708 include GMRs.
- FIG. 8 B shows a curve of the angle error versus detected angle of magnetic field.
- FIG. 9 another example of a configuration to reduce a stray magnetic field effect is a configuration 900 .
- the configuration 900 is similar to the configuration 600 except the configuration 900 includes a sine coil 902 a and a sine coil 902 b .
- the sine coils 902 a , 902 b are perpendicular to the cosine coils 602 a , 602 b .
- the emitter 702 modulates the sine coils 902 a , 902 b at a modulation frequency.
- the sine coils 902 a , 902 b are also attached to the rotating device that rotates about the axis 610 .
- the coils 602 a , 602 b , 902 a , 902 b may be activated by time and/or frequency multiplex.
- the coils 602 a , 602 b , 902 a , 902 b may be modulated at the same time or the cosine coils 602 a , 602 b may be modulated at first time and the sine coils 902 a , 902 b may be modulated at a second time different from the first time.
- the cosine coils 602 a , 602 b may be modulated at the same modulation frequency, or the cosine coils 602 a , 602 b may be modulated at a first modulation frequency and the sine coils 902 a , 902 b may be modulated at a second modulation frequency different from the first modulation frequency. In one example, the cosine coils 602 a , 602 b may be modulated at the first time at the first modulation frequency and the sine coils 902 a , 902 b may modulated at the second time at the second frequency modulation.
- a circuit representation of the configuration 900 is a circuit 1000 .
- the circuit 1000 is similar to the circuit 700 except the circuit 1000 includes an angle sensor 604 ′′ but does not include the sine bridge 708 .
- the configuration 1100 includes an angle sensor 1120 with outward magnetized pole magnets 1102 (e.g., an outward magnetized pole magnet 1102 a and an outward magnetized pole magnet 1102 b ) and inward magnetized pole magnets 1104 (e.g., an inward magnetized pole magnet 1104 a and an inward magnetized pole magnet 1104 b ).
- the angle sensor 1120 is located at the center of the magnet target (i.e., the center between the magnetized pole magnets 1102 a , 1102 b , 1104 a , 1104 b ).
- the outward magnetized pole magnet 1102 a is positioned opposite the outward magnetized pole magnet 1102 b , and the angle sensor 1120 is positioned between the outward magnetized pole magnets 1102 a , 1102 b . Magnetization of each of the outward magnetized pole magnet 1102 a , 1102 b points away from the angle sensor 1120 .
- the inward magnetized pole magnet 1104 a is positioned opposite the inward magnetized pole magnet 1104 b , and the angle sensor 1120 is positioned between the inward magnetized pole magnets 1104 a , 1104 b . Magnetization of each of the inward magnetized pole magnet 1104 a , 1104 b points towards the angle sensor 1120 .
- the angle sensor 1120 includes TMR elements. In another example, the angle sensor 1120 includes GMR elements. In a further example, the angle sensor 1120 includes magnetometers. In further examples, TMR elements, GMR elements or magnetometers may be in one or more bridges included with the angle sensor 1120 .
- FIG. 12 depicts a diagram 1200 inward and outward magnetized pole magnets 1102 a , 1102 b , 1104 a , 1104 b overlaid with a quiver plot and overlaid with a level plot of magnetic field amplitudes.
- there is an out of plane component of the magnetic field For example, the magnetized poles 1102 b , 1104 b have a magnetization tilted 15° out of the page while the magnetized poles 1102 a , 1104 a have a magnetization tiled 15° into the page.
- Hall plates may be located at locations J 1202 , K 1204 , L 1206 and M 1208 that can measure the out of plane component of the magnetic field.
- FIG. 13 depicts a diagram 1200 ′ which is the same as FIG. 12 , except the diagram designates locations where magnetoresistance elements may be placed to reduce the effects of a stray magnetic field.
- two magnetoresistance elements may be placed at each location 1302 , 1304 , 1306 , 1308 and locations 1302 , 1304 , 1306 , 1308 are equally spaced a part around a circle (not shown) so that a line (not shown) from location A to location B is perpendicular to and bisects a line (not shown) from C to D.
- the angle sensor 1120 may include bridges such as a cosine bridge 1402 and a sine bridge 1404 .
- the cosine bridge 1402 includes a magnetoresistance element 1302 a and a magnetoresistance element 1304 b in series with each other and in parallel with a magnetoresistance element 1304 a and a magnetoresistance element 1302 b .
- the magnetoresistance element 1302 a and the magnetoresistance element 1302 b are located at the location A 1302 ( FIG. 13 ), and the magnetoresistance element 1304 a and the magnetoresistance element 1304 b are located at the location B 1304 ( FIG. 13 ).
- the sine bridge 1404 includes a magnetoresistance element 1306 a and a magnetoresistance element 1308 b in series with each other and in parallel with a magnetoresistance element 1308 a and a magnetoresistance element 1306 b .
- the magnetoresistance element 1306 a and the magnetoresistance element 1306 b are located at the location C 1306 ( FIG. 13 ), and the magnetoresistance element 1308 a and the magnetoresistance element 1308 b are located at the location D 1308 ( FIG. 13 ).
- a curve 1527 represents a Hall plate signal that takes the difference between location J 1202 and location K 1204 and a curve 1529 represents a Hall plate signal that takes the difference between location L 1206 and location K 1208 .
- a graph 1550 includes a curve 1552 depicting the output angle of the angle sensor 1120 .
- the curve 1150 is derived using the curves 1502 , 1504 , 1527 , 1529 .
- the curves 1527 and 1529 are used to determine if the target angle is between 0° and 180° or between 180° and 360°.
- a graph 1575 includes a curve 1577 depicting the angle error and is derived from the curve 1552 .
- a graph 1600 depicts worse angle error due to different stray magnetic field amplitudes for different misplacements of the angle sensor from the center of the target.
- Worst angle error means a worst case between all combinations of target phase and stray field phase.
- the stray magnetic field induced error is lower than the accuracy before any corrections for misplacement of the sensor from the center of the magnet target (i.e., the center between the magnetized pole magnets 1102 a , 1102 b , 1104 a , 1104 b.
- a curve 1602 represents the maximum angle error due to a rotating 10 Oersted (Oe) stray field versus misplacement in the X-direction and a curve 1604 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the Y-direction
- a curve 1612 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the X-direction
- a curve 1614 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the Y-direction
- a curve 1622 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the X-direction
- a curve 1624 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the Y-direction
- a curve 1632 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the X-direction
- FIG. 17 depicts a diagram 1200 ′′ which is the same as FIG. 13 , except the diagram designates additional locations where magnetoresistance elements of an angle sensor may be placed to reduce the effects of a stray magnetic field.
- two magnetoresistance elements may be placed at each location 1702 - 1716 .
- the angle sensor 1120 may include bridges such as a cosine bridge 1802 and a sine bridge 1804 .
- the cosine bridge 1802 includes a magnetoresistance element 1702 a , a magnetoresistance element 1704 a , a magnetoresistance element 1706 b , and a magnetoresistance element 1708 b in series with each other and in parallel a magnetoresistance element 1702 b , a magnetoresistance element 1704 b , a magnetoresistance element 1706 a , and a magnetoresistance element 1708 a.
- the magnetoresistance element 1702 a and the magnetoresistance element 1702 b are located at the location A 1 1702 ( FIG. 17 ), and the magnetoresistance element 1704 a and the magnetoresistance element 1704 b are located at the location A 2 1704 ( FIG. 17 ).
- the magnetoresistance element 1706 a and the magnetoresistance element 1706 b are located at the location B 1 1706 ( FIG. 17 ), and the magnetoresistance element 1708 a and the magnetoresistance element 1708 b are located at the location B 2 1708 ( FIG. 17 ).
- the sine bridge 1804 includes a magnetoresistance element 1710 a , a magnetoresistance element 1712 a , a magnetoresistance element 1714 b , and a magnetoresistance element 1716 b in series with each other and in a magnetoresistance element 1710 b , a magnetoresistance element 1712 b , a magnetoresistance element 1714 a , and a magnetoresistance element 1716 a.
- the magnetoresistance element 1710 a and the magnetoresistance element 1710 b are located at the location C 1 1710 ( FIG. 17 ), and the magnetoresistance element 1712 a and the magnetoresistance element 1712 b are located at the location C 2 1712 ( FIG. 17 ).
- the magnetoresistance element 1714 a and the magnetoresistance element 1714 b are located at the location D 1 1714 ( FIG. 17 ), and the magnetoresistance element 1716 a and the magnetoresistance element 1716 b are located at the location D 2 1716 ( FIG. 17 ).
- a graph 1900 includes a curve 1902 .
- the curve 1902 indicates a maximum angular error over a full rotation versus a composite angle.
- the composite angle is half the angle of a split of: the MR elements 1702 a , 1702 b , 1704 a , 1704 b at location A 1 1702 and A 2 1704 ; or the MR elements 1706 a , 1706 b , 1708 a , 1708 b at location B 1 1706 and location B 2 1708 ; or the MR elements 1710 a , 1710 b , 1712 a , 1712 b at location C 1 1710 and location C 2 1712 ; or the MR elements 1714 a , 1714 b , 1716 a , 1716 b at location D 1 1714 and location D 2 1716 .
- choosing a composite angle of about 30° is at least three times better than choosing a composite angle of 50°.
- a graph 2000 includes curves 2002 , 2004 .
- the curve 2002 shows the maximum angle error over a full rotation versus X-axis misplacement of the angle sensor.
- the curve 2004 shows the maximum angle error over a full rotation versus Y-axis misplacement of the angle sensor.
- a graph 2100 depicts worse angle error due to different stray field amplitudes for different misplacements of the angle sensor from the center of the target.
- the stray magnetic field induced error is lower than the accuracy before any corrections for misplacement of the sensor from the center of the magnet target (i.e., the center between the magnetized pole magnets 1102 a , 1102 b , 1104 a , 1104 b.
- a curve 2102 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the X-direction and a curve 2104 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the Y-direction
- a curve 2112 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the X-direction
- a curve 2114 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the Y-direction
- a curve 2122 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the X-direction
- a curve 2124 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the Y-direction
- a curve 2132 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the X-direction and a curve 21
- FIG. 22 depicts a diagram 1200 ′′′ which is the same as FIG. 17 , except the diagram designates additional locations where magnetoresistance elements of an angle sensor may be placed to reduce the effects of a stray magnetic field.
- there are eighteen locations e.g., a location 2202 ) arranged in a circle wherein magnetoresistance elements may be placed.
- a graph 2300 depicts the target phase versus angle error for different numbers of magnetoresistance elements used. For example, a curve 2302 depicts using eight magnetoresistance elements, a curve 2304 depicts using sixteen magnetoresistance elements and a curve 2306 depicts using thirty-two magnetoresistance elements.
- a graph 2400 includes curves 2402 , 2004 .
- the curve 2402 shows the maximum angle error over a full rotation versus X-axis misplacement of the angle sensor.
- the curve 2404 shows the maximum angle error over a full rotation versus Y-axis misplacement of the angle sensor.
- a graph 2500 depicts worse angle error due to different stray field amplitudes for different misplacements of the angle sensor from the center of the target.
- the stray magnetic field induced error is lower than the accuracy before any corrections for misplacement of the sensor from the center of the magnet target (i.e., the center between the magnetized pole magnets 1102 a , 1102 b , 1104 a , 1104 b.
- a curve 2502 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the X-direction and a curve 2504 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the Y-direction
- a curve 2512 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the X-direction
- a curve 2514 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the Y-direction
- a curve 2522 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the X-direction
- a curve 2524 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the Y-direction
- a curve 2532 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the X-direction and a curve 25
- An angle of rotation of the target ⁇ can be achieved for the embodiments in FIGS. 13 , 17 and 22 .
- a mapping of the signal across the MR elements is acquired. After acquiring the mapping of signals across the MR elements, values are stored in a vector called Res. Then the following convolution operation can be run:
- Resi is the resistance (may be conductance also) of the i th MR element in the vector and Xi is the angular position of the i th MR element on the die.
- C is computed as a complex number but the exact same results can be obtained by running two convolutions; one with a cosine (this would provide the real part of C) and one with a sine (this would provide the imaginary part of C). Also, the cosine and sine used for the convolution can be stored as two N elements vectors in memory to reduce algorithm execution time.
- the angle of rotation of the target ⁇ can be extracted with the following operation:
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Abstract
Description
- This is a Divisional application and claims the benefit of and priority to U.S. patent application Ser. No. 16/800,229, filed Feb. 25, 2020, entitled “REDUCING STRAY MAGNETIC FIELD EFFECT ON AN ANGLE SENSOR,” which is incorporated herein by reference in its entirety.
- Typically, a magnetic-field angle sensor measures a direction of a magnetic-field vector through 360° in an x-y plane. In one example, a magnetic-field angle sensor may be used to detect an angular position of a rotating magnet. The presence of stray magnetic fields (i.e., magnetic fields coming from other sources than a desired target) can increase an angle error of the angle sensor. Generally, the angle error is defined to be the difference between an actual position of a magnet and a position of the magnet as measured by the angle sensor.
- In one aspect, an angle sensor includes a first linear sensor and a second linear sensor. A first magnetic-field direction of a target magnet measured by the first linear sensor is substantially equal to a second magnetic-field direction of the target magnet measured by the second linear sensor. The first linear sensor, the second linear sensor and the target magnet are on an axis. The angle sensor determines an angle of a magnetic field.
- In another aspect, an angle sensor configuration includes a first coil, a second coil parallel to the first coil and an angle sensor disposed between the first coil and the second coil. The angle sensor configured to determine an angle of a magnetic field.
- In a further aspect, an angle sensor configuration includes an angle sensor, a first magnet having a first outward magnetized pole along a first axis away from the angle sensor and a second magnet opposite the first magnetic. The second magnet has a second outward magnetized pole along the first axis away from the angle sensor. The angle sensor configuration further includes a third magnet having a first inward magnetized pole along a second axis toward the angle sensor and a fourth magnet opposite the third magnetic. The third magnet has a second inward magnetized pole along the second axis toward the angle sensor. The angle sensor is disposed between the first, second, third and fourth magnets. The angle sensor configured to determine an angle of a magnetic field.
- The foregoing features may be more fully understood from the following description of the drawings. The drawings aid in explaining and understanding the disclosed technology. Since it is often impractical or impossible to illustrate and describe every possible embodiment, the provided figures depict one or more illustrative embodiments. Accordingly, the figures are not intended to limit the scope of the broad concepts, systems and techniques described herein. Like numbers in the figures denote like elements.
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FIG. 1 is a diagram of an example of stacked two-dimensional (2D) linear sensors forming an angle sensor to reduce a stray magnetic field effect; -
FIG. 2 is a diagram of example of stacked 2D linear sensor package configuration; -
FIG. 3 is a diagram of an example of magnetic field directions for one of the stacked 2D linear sensors closer to the magnet target; -
FIG. 4 is a diagram of an example of magnetic field directions for one of the stacked 2D linear sensors further to the magnet target; -
FIG. 5 is a diagram of an example of magnetic field directions for the 2D stacked linear sensors; -
FIG. 6 is a diagram of an example of an angle sensor configuration with two cosine coils to reduce a stray magnetic field effect; -
FIG. 7 is a diagram of an example of a circuit representation ofFIG. 6 having two bridges; -
FIG. 8A is a graph of an example of outputs of the two bridges inFIG. 7 ; -
FIG. 8B is a graph of an example of the angle error for the angle sensor configuration ofFIG. 6 ; -
FIG. 9 is a diagram of another example of an angle sensor configuration with two cosine and two sine coils to reduce a stray magnetic field effect; -
FIG. 10 is a circuit representation ofFIG. 9 having one bridge; -
FIG. 11 is a diagram of an example of an angle sensor configuration with inward and outward magnetized pole magnets to reduce a stray magnetic field effect; -
FIG. 12 is a diagram of the inward and outward magnetized pole magnets ofFIG. 11 overlaid with an example of a level plot of magnetic field amplitudes; -
FIG. 13 is a diagram ofFIG. 12 with example locations for magnetoresistance elements; -
FIG. 14A is a diagram of an example of a cosine bridge at locations inFIG. 13 ; -
FIG. 14B is a diagram of an example of a sine bridge at locations inFIG. 13 ; -
FIG. 15A is a graph of example of outputs for the sine and cosine bridges ofFIGS. 14A and 14B ; -
FIG. 15B is a graph of example of Hall signals; -
FIG. 15C is a graph of an example of an output signal of an angle sensor; -
FIG. 15D is a graph of an example of an angle error for the angle sensor configuration ofFIG. 11 ; -
FIG. 16 is a graph of an example of stray magnetic field induced angle error for the configuration inFIG. 11 ; -
FIG. 17 is a diagram ofFIG. 13 with additional examples locations for magnetoresistance elements; -
FIG. 18A is a diagram of an example of a cosine bridge at locations inFIG. 17 ; -
FIG. 18B is a diagram of an example of a sine bridge at locations inFIG. 17 ; -
FIG. 19 is a graph of an example of maximum error over a composite angle; -
FIG. 20 is a graph of an example of misplacement induced angle error; -
FIG. 21 is a graph of an example of stray magnetic field induced angle error for the configuration inFIG. 17 ; -
FIG. 22 is a diagram ofFIG. 17 with additional examples locations for magnetoresistance elements arranged in a circle; -
FIG. 23 is a graph of an example of angle error versus target phase for different number of magnetoresistance elements used; -
FIG. 24 is a graph of an example of misplacement induced angle error; and -
FIG. 25 is a graph of an example of stray magnetic field induced angle error for the configuration inFIG. 22 . - Described herein are techniques to reduce a stray magnetic field (sometimes referred to as a “stray field”) effect on an angle sensor. A reduced stray magnetic field effect contributes to reducing angle errors in the angle sensor.
- As used herein, the term “magnetic-field sensing element” is used to describe a variety of electronic elements that can sense a magnetic field. The magnetic-field sensing element can be, but is not limited to, a Hall Effect element, a magnetoresistance element, or a magnetotransistor. As is known, there are different types of Hall Effect elements, for example, a planar Hall element, a vertical Hall element, and a Circular Vertical Hall (CVH) element. As is also known, there are different types of magnetoresistance elements, for example, a semiconductor magnetoresistance element such as Indium Antimonide (InSb), a giant magnetoresistance (GMR) element, an anisotropic magnetoresistance element (AMR), a tunneling magnetoresistance (TMR) element, and a magnetic tunnel junction (MTJ). The magnetic field sensing element may be a single element or, alternatively, may include two or more magnetic field sensing elements arranged in various configurations, e.g., a half bridge or full (Wheatstone) bridge. Depending on the device type and other application requirements, the magnetic field sensing element may be a device made of a type IV semiconductor material such as Silicon (Si) or Germanium (Ge), or a type III-V semiconductor material like Gallium-Arsenide (GaAs) or an Indium compound, e.g., Indium-Antimonide (InSb).
- As is known, some of the above-described magnetic-field sensing elements tend to have an axis of maximum sensitivity parallel to a substrate that supports the magnetic-field sensing element, and others of the above-described magnetic-field sensing elements tend to have an axis of maximum sensitivity perpendicular to a substrate that supports the magnetic-field sensing element. In particular, planar Hall elements tend to have axes of sensitivity perpendicular to a substrate, while metal based or metallic magnetoresistance elements (e.g., GMR, TMR, AMR) and vertical Hall elements tend to have axes of sensitivity parallel to a substrate.
- Referring to
FIG. 1 , in one example, two-dimensional (2D) linear sensors may be used together to function like an angle sensor. For example, a first two-dimensional (2D)linear sensor 14 and a second 2Dlinear sensor 18 are vertically aligned on anaxis 20 with amagnet target 10. Anarrow 12 indicates an in-plane magnetization of themagnet target 10. In one example, the first 2Dlinear sensor 14 is disposed along a first plane (not shown) and the second linear sensor is disposed along a second plane (not shown) and the first plane and the second plane are each perpendicular to theaxis 20. - An
ellipse 22 represents a high-field magnetic flux line and anellipse 24 represents a low-field magnetic flux line. Thus, the first 2Dlinear sensor 14 experiences a higher magnetic field amplitude than the second 2Dlinear sensor 18. The magnetic field amplitude decreases when distance increases. - In one embodiment, the 2D
linear sensors linear sensors - The stacked 2D
linear sensors magnetic target 10 at two locations where the magnetic field direction is identical at both locations, but the magnetic field amplitude varies. As will be further described herein, the useful signal is the amplitude difference of the detected magnetic fields from these two locations. - Referring to
FIG. 2 , an example of a configuration to package the first and second 2Dlinear sensors package 200. Thepackage 200 includes afirst die 32 having the first 2Dlinear sensor 14 on a top surface, asecond die 36 having the second 2D linear sensor on a bottom surface and a printed circuit board (PCB) 42. - A
spacer 28 separates (e.g., by about 25 microns) the first die 32 from thesecond die 36. In one example thesecond die 36 may be a flip-chip structure that is connected to thePCB 42 usingsolder balls 34. In one embodiment, abonding wire 44 connects thePCB 42 to the first 2Dlinear sensor 14. In one example, the firstlinear sensor 14 and the secondlinear sensor 18 are spaced apart by about 1 millimeter. In other embodiments, multiple bonding wires (not shown) connect thePCB 42 to the first 2Dlinear sensor 14. - The
package 200 is an example of placing the 2Dlinear sensors - In one example, each of the 2D
linear sensors -
FIG. 3 depicts fields sensed by the first 2Dlinear sensor 14. Anarrow 302 indicates a target magnetic field from themagnetic target 10 and anarrow 306 represents a stray magnetic field. Anarrow 304 represents the total field (i.e., the targetmagnetic field arrow 302 plus the stray field arrow 306). -
FIG. 4 depicts fields sensed by the second 2Dlinear sensor 18. Anarrow 402 indicates a target magnetic field from themagnetic target 10 and anarrow 406 represents the stray magnetic field. Anarrow 404 represents the total field (i.e., the targetmagnetic field arrow 402 plus the stray magnetic field arrow 406).FIGS. 3 and 4 are not drawn to the same scale. That is,arrow 306 andarrow 406 should be the same size since the magnetic stray field is in a common mode (i.e., the same in all space of the application). -
FIG. 5 depicts magnetic fields experienced by the first 2Dlinear sensor 14 and the second 2Dlinear sensor 18. Thearrows arrows 302, 402) is depicted by anarrow 500 parallel to thearrows magnetic field arrows linear sensor 14 and the second 2Dlinear sensor 18 respectively are not parallel to the targetmagnetic fields linear sensors magnetic fields - Referring to
FIG. 6 , another example of a configuration to reduce stray magnetic field effects is aconfiguration 600. Theconfiguration 600 includes anangle sensor 604 between acosine coil 602 a and acosine coil 602 b. In this configuration, detection of a magnetic field occurs at higher frequencies where there are no stray magnetic fields. The magnetic field is modulated using the cosine coils 600 a, 600 b as an emitter and the angle of the magnetic field is detected. Thecoils axis 610. In one embodiment, thecoils - Referring to
FIG. 7 , a circuit representation of the configuration 600 (FIG. 6 ) is acircuit 700. The circuit includes thecoils angle sensor 604′, which is an example of the angle sensor 604 (FIG. 6 ). Theangle sensor 604′ includes amodulator 702 that modulates thecoils - The
angle sensor 604′ also includes acosine bridge 706 and asine bridge 708 that are modulated by themodulator 702 by the modulation frequency. Thecosine bridge 706 and thesine bridge 708 are perpendicular to one another and have a reference (sensitive) axis perpendicular to one another. That is, thecosine bridge 706 is most sensitive along an x-axis and thesine bridge 708 is most sensitive along the y-axis. - The
cosine bridge 706 and thesine bridge 708 demodulate the magnetic field signal generated by the cosine coils 602 a, 602 b. By demodulating the outputs of the two bridges the x-axis and y-axis projections of the detected magnetic field are obtained, i.e. the cosine and the sine of the measured magnetic field angle (multiplied by the field amplitude). - Referring to
FIG. 8A , an example of an output of thecosine bridge 706 is depicted by thecurve 802 and an example of an output of thesine bridge 708 is depicted by thecurve 804. In this example, thecosine bridge 706 and thecosine bridge 708 include GMRs.FIG. 8B shows a curve of the angle error versus detected angle of magnetic field. - Referring to
FIG. 9 , another example of a configuration to reduce a stray magnetic field effect is aconfiguration 900. Theconfiguration 900 is similar to theconfiguration 600 except theconfiguration 900 includes asine coil 902 a and asine coil 902 b. The sine coils 902 a, 902 b are perpendicular to the cosine coils 602 a, 602 b. Theemitter 702 modulates the sine coils 902 a, 902 b at a modulation frequency. The sine coils 902 a, 902 b are also attached to the rotating device that rotates about theaxis 610. - In one example, the
coils coils - Referring to
FIG. 10 , a circuit representation of the configuration 900 (FIG. 9 ) is acircuit 1000. Thecircuit 1000 is similar to thecircuit 700 except thecircuit 1000 includes anangle sensor 604″ but does not include thesine bridge 708. - Referring to
FIG. 11 , a further example of a configuration to reduce a stray magnetic field effect is aconfiguration 1100. Theconfiguration 1100 includes anangle sensor 1120 with outward magnetized pole magnets 1102 (e.g., an outwardmagnetized pole magnet 1102 a and an outwardmagnetized pole magnet 1102 b) and inward magnetized pole magnets 1104 (e.g., an inwardmagnetized pole magnet 1104 a and an inwardmagnetized pole magnet 1104 b). Theangle sensor 1120 is located at the center of the magnet target (i.e., the center between themagnetized pole magnets - The outward
magnetized pole magnet 1102 a is positioned opposite the outwardmagnetized pole magnet 1102 b, and theangle sensor 1120 is positioned between the outwardmagnetized pole magnets magnetized pole magnet angle sensor 1120. - The inward
magnetized pole magnet 1104 a is positioned opposite the inwardmagnetized pole magnet 1104 b, and theangle sensor 1120 is positioned between the inwardmagnetized pole magnets magnetized pole magnet angle sensor 1120. - In one example, the
angle sensor 1120 includes TMR elements. In another example, theangle sensor 1120 includes GMR elements. In a further example, theangle sensor 1120 includes magnetometers. In further examples, TMR elements, GMR elements or magnetometers may be in one or more bridges included with theangle sensor 1120. -
FIG. 12 depicts a diagram 1200 inward and outwardmagnetized pole magnets magnetized poles magnetized poles locations J 1202,K 1204,L 1206 and M 1208 that can measure the out of plane component of the magnetic field. -
FIG. 13 depicts a diagram 1200′ which is the same asFIG. 12 , except the diagram designates locations where magnetoresistance elements may be placed to reduce the effects of a stray magnetic field. In this embodiment there are four locations: alocation A 1302, alocation B 1304 oppositelocation A 1302, alocation C 1306 and alocation D 1308 opposite thelocation C 1308. In this embodiment, two magnetoresistance elements may be placed at eachlocation locations - Referring to
FIGS. 14A and 14B , the angle sensor 1120 (FIG. 11 ) may include bridges such as acosine bridge 1402 and asine bridge 1404. InFIG. 14A thecosine bridge 1402 includes amagnetoresistance element 1302 a and amagnetoresistance element 1304 b in series with each other and in parallel with amagnetoresistance element 1304 a and amagnetoresistance element 1302 b. Themagnetoresistance element 1302 a and themagnetoresistance element 1302 b are located at the location A 1302 (FIG. 13 ), and themagnetoresistance element 1304 a and themagnetoresistance element 1304 b are located at the location B 1304 (FIG. 13 ). - In
FIG. 14B thesine bridge 1404 includes amagnetoresistance element 1306 a and amagnetoresistance element 1308 b in series with each other and in parallel with amagnetoresistance element 1308 a and amagnetoresistance element 1306 b. Themagnetoresistance element 1306 a and themagnetoresistance element 1306 b are located at the location C 1306 (FIG. 13 ), and themagnetoresistance element 1308 a and themagnetoresistance element 1308 b are located at the location D 1308 (FIG. 13 ). - Referring to
FIG. 15A , an example of an output of thecosine bridge 1402 is depicted by thecurve 1502 and an example of an output of thesine bridge 1404 is depicted by thecurve 1504. Referring toFIG. 15B , acurve 1527 represents a Hall plate signal that takes the difference betweenlocation J 1202 andlocation K 1204 and acurve 1529 represents a Hall plate signal that takes the difference betweenlocation L 1206 andlocation K 1208. - Referring to
FIG. 15C , agraph 1550 includes acurve 1552 depicting the output angle of theangle sensor 1120. The curve 1150 is derived using thecurves cosine curve 1502 and thesine curve 1504 have two periods between −180° and 180°, thecurves FIG. 15D , agraph 1575 includes acurve 1577 depicting the angle error and is derived from thecurve 1552. - Referring to
FIG. 16 , agraph 1600 depicts worse angle error due to different stray magnetic field amplitudes for different misplacements of the angle sensor from the center of the target. Worst angle error means a worst case between all combinations of target phase and stray field phase. The stray magnetic field induced error is lower than the accuracy before any corrections for misplacement of the sensor from the center of the magnet target (i.e., the center between themagnetized pole magnets - For example, a
curve 1602 represents the maximum angle error due to a rotating 10 Oersted (Oe) stray field versus misplacement in the X-direction and acurve 1604 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the Y-direction, acurve 1612 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the X-direction and acurve 1614 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the Y-direction, acurve 1622 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the X-direction and acurve 1624 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the Y-direction, and acurve 1632 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the X-direction and acurve 1634 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the Y-direction. - Referring to
FIG. 17 , depicts a diagram 1200″ which is the same asFIG. 13 , except the diagram designates additional locations where magnetoresistance elements of an angle sensor may be placed to reduce the effects of a stray magnetic field. In this embodiment there are eight locations: alocation A 1 1702, alocation A 2 1704, alocation B 1 1706, alocation B 2 1708, alocation C 1 1710, alocation C 2 1712, alocation D 1 1714 and alocation D 2 1716. In this embodiment, two magnetoresistance elements may be placed at each location 1702-1716. - Referring to
FIGS. 18A and 18B , the angle sensor 1120 (FIG. 11 ) may include bridges such as acosine bridge 1802 and asine bridge 1804. InFIG. 18A thecosine bridge 1802 includes amagnetoresistance element 1702 a, amagnetoresistance element 1704 a, amagnetoresistance element 1706 b, and amagnetoresistance element 1708 b in series with each other and in parallel amagnetoresistance element 1702 b, amagnetoresistance element 1704 b, amagnetoresistance element 1706 a, and amagnetoresistance element 1708 a. - The
magnetoresistance element 1702 a and themagnetoresistance element 1702 b are located at the location A1 1702 (FIG. 17 ), and themagnetoresistance element 1704 a and themagnetoresistance element 1704 b are located at the location A2 1704 (FIG. 17 ). Themagnetoresistance element 1706 a and themagnetoresistance element 1706 b are located at the location B1 1706 (FIG. 17 ), and themagnetoresistance element 1708 a and themagnetoresistance element 1708 b are located at the location B2 1708 (FIG. 17 ). - In
FIG. 18B thesine bridge 1804 includes amagnetoresistance element 1710 a, amagnetoresistance element 1712 a, amagnetoresistance element 1714 b, and amagnetoresistance element 1716 b in series with each other and in amagnetoresistance element 1710 b, amagnetoresistance element 1712 b, amagnetoresistance element 1714 a, and amagnetoresistance element 1716 a. - The
magnetoresistance element 1710 a and themagnetoresistance element 1710 b are located at the location C1 1710 (FIG. 17 ), and themagnetoresistance element 1712 a and themagnetoresistance element 1712 b are located at the location C2 1712 (FIG. 17 ). Themagnetoresistance element 1714 a and themagnetoresistance element 1714 b are located at the location D1 1714 (FIG. 17 ), and themagnetoresistance element 1716 a and themagnetoresistance element 1716 b are located at the location D2 1716 (FIG. 17 ). - Referring to
FIG. 19 , agraph 1900 includes acurve 1902. Thecurve 1902 indicates a maximum angular error over a full rotation versus a composite angle. The composite angle is half the angle of a split of: theMR elements location A 1 1702 and A2 1704; or theMR elements location B 1 1706 andlocation B 2 1708; or theMR elements location C 1 1710 andlocation C 2 1712; or theMR elements location D 1 1714 andlocation D 2 1716. Thus, in this example, choosing a composite angle of about 30° is at least three times better than choosing a composite angle of 50°. - Referring to
FIG. 20 , agraph 2000 includescurves curve 2002 shows the maximum angle error over a full rotation versus X-axis misplacement of the angle sensor. Thecurve 2004 shows the maximum angle error over a full rotation versus Y-axis misplacement of the angle sensor. - Referring to
FIG. 21 , agraph 2100 depicts worse angle error due to different stray field amplitudes for different misplacements of the angle sensor from the center of the target. When compared toFIG. 20 , the stray magnetic field induced error is lower than the accuracy before any corrections for misplacement of the sensor from the center of the magnet target (i.e., the center between themagnetized pole magnets - For example, a
curve 2102 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the X-direction and acurve 2104 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the Y-direction, acurve 2112 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the X-direction and acurve 2114 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the Y-direction, acurve 2122 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the X-direction and acurve 2124 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the Y-direction, and acurve 2132 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the X-direction and acurve 2134 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the Y-direction at. -
FIG. 22 depicts a diagram 1200″′ which is the same asFIG. 17 , except the diagram designates additional locations where magnetoresistance elements of an angle sensor may be placed to reduce the effects of a stray magnetic field. In this embodiment there are eighteen locations (e.g., a location 2202) arranged in a circle wherein magnetoresistance elements may be placed. - Referring to
FIG. 23 , agraph 2300 depicts the target phase versus angle error for different numbers of magnetoresistance elements used. For example, acurve 2302 depicts using eight magnetoresistance elements, acurve 2304 depicts using sixteen magnetoresistance elements and acurve 2306 depicts using thirty-two magnetoresistance elements. - Referring to
FIG. 24 , agraph 2400 includescurves curve 2402 shows the maximum angle error over a full rotation versus X-axis misplacement of the angle sensor. Thecurve 2404 shows the maximum angle error over a full rotation versus Y-axis misplacement of the angle sensor. - Referring to
FIG. 25 , agraph 2500 depicts worse angle error due to different stray field amplitudes for different misplacements of the angle sensor from the center of the target. When compared toFIG. 24 , the stray magnetic field induced error is lower than the accuracy before any corrections for misplacement of the sensor from the center of the magnet target (i.e., the center between themagnetized pole magnets - For example, a
curve 2502 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the X-direction and acurve 2504 represents the maximum angle error due to a rotating 10 Oe stray field versus misplacement in the Y-direction, acurve 2512 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the X-direction and acurve 2514 represents the maximum angle error due to a rotating 20 Oe stray field versus misplacement in the Y-direction, acurve 2522 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the X-direction and acurve 2524 represents the maximum angle error due to a rotating 30 Oe stray field versus misplacement in the Y-direction, and acurve 2532 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the X-direction and acurve 2534 represents the maximum angle error due to a rotating 40 Oe stray field versus misplacement in the Y-direction. - An angle of rotation of the target θ can be achieved for the embodiments in
FIGS. 13, 17 and 22 . A mapping of the signal across the MR elements is acquired. After acquiring the mapping of signals across the MR elements, values are stored in a vector called Res. Then the following convolution operation can be run: -
- where N is the number of MR elements, Resi is the resistance (may be conductance also) of the ith MR element in the vector and Xi is the angular position of the ith MR element on the die.
- In this case C is computed as a complex number but the exact same results can be obtained by running two convolutions; one with a cosine (this would provide the real part of C) and one with a sine (this would provide the imaginary part of C). Also, the cosine and sine used for the convolution can be stored as two N elements vectors in memory to reduce algorithm execution time.
- The angle of rotation of the target θ can be extracted with the following operation:
-
- Elements of different embodiments described herein may be combined to form other embodiments not specifically set forth above. Various elements, which are described in the context of a single embodiment, may also be provided separately or in any suitable subcombination. Other embodiments not specifically described herein are also within the scope of the following claims.
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